The present invention relates to a brake booster for the braking system of a motor vehicle.
Known brake boosters generally comprise a housing, a diaphragm sealingly secured in the housing to define a front chamber and a rear chamber, a movable piston attached to the diaphragm, an input member connectable to the brake pedal, and an output member connectable to a piston of a master cylinder. A deformable reaction disc is positioned between the output member and the piston. When the booster is operated, the reaction disc receives the output force and deforms such as to tend to push back on the input member.
The object of the present invention is to provide an improvement in the performance of such a brake booster.
A brake booster in accordance with the present invention comprises a housing; a diaphragm sealingly mounted inside the housing to define separate chambers inside the housing; a piston having a longitudinal axis, the piston being secured to the diaphragm, extending out of the housing, and being movable along the axis relative to the housing; a reaction member mounted in the piston; an input member extending into the piston and engageable with one side of the reaction member; a disc engageable with the other side of the reaction member; a Belleville spring mounted on the disc; an annular member positioned radially outwards of the disc and engageable with the other side of the reaction member; an output member engaging the Belleville spring, the Belleville spring biasing the output member away from the reaction disc in the rest position of the booster such that only the disc acts on the output member below a predetermined input force on the input member, and such that at or above the predetermined input force the bias of the Belleville spring is overcome and both the disc and the annular member act on the output member.
The present invention provides a brake booster in which the ratio of the booster changes at a predetermined input force, when the Belleville spring load is overcome to increase the effective contact area between the output member and the reaction member. This design provides increased brake pressure, for example, during panic braking, with a simple and easy arrangement.